Method of providing glass fibers with plural superimposed different oxide coatings and products thereby produced



D. LABINO 2,839,424 METHOD OF PROVIDING GLASS FIBERS WITH PLURAL June 17, 1958 SUPERIMPOSED DIFFERENT OXIDE COATINGS AND PRODUCTS THEREBY PRODUCED Filed Aug. 10, 1955 m ol INVENT OR. DOMINIGK LABINO Z0446 fdwopz AT TORNEYS ite rates Patent 2,839,424 Patented June 17, 1958 Dominick Labino, Toledo, Ohio, assignor to L-O F Glass Fibers (Iompany, Toledo, Ohio, a corporation of Ohio Application August 10, 1955, Serial No. 527,610 Claims. (Cl. 117-455) This invention relates to temperature-resistant fibrous products and to methods of producing the same.

T he invention particularly contemplates the production of flexible fibers which are useful as insulation material in high temperature applications such as jet airplane insulation and fire-entry suits.

The invention further contemplates the provision of diameters are in the submicron range. Fibers having a diameter of 1 micron and below thus constitute the preferred embodiment although fibers up to a diameter of about 1.5 microns have some utility. These fine fibers are attained by flame-blowing filaments of alkali silicates to attain a mass of extremely short fibers of the noted diameters which contain alkali in a form which is capable relatively inflexible fibrous bodies having utility as light weight refractory bricks, for example.

The invention also is directed to providing novel methods of manufacture of the flexible and inflexible products.

In the practice of the invention fibers of an alkali silicate are treated with a medium such as anaqueous solution of a chloride of calcium, zinc or barium. The metal of the chloride replaces a portion of the alkali in the fiber by ion exchange while the water of the so1ution is also incorporated in the fiber to a material extent.

I have found that if the fiber thus formed is heated sufiiciently to drive off the water constituent, that the porous fiber remaining is highly receptive to solutions of solutes, which solutes upon heating yield temperatureresistant oxides. Such solutes are chromic anhydridc (CrO cobalt nitrate, zinc nitrate or chloride, and aluminum nitrate or sulfate, for example. Thus by subjecting the fiber which has been freed of all water to a solution of one or more of these latter constituents, the constituents are picked up by and become an integral part of the fiber.

The utilization of agents such as the aqueous chloride solutions and the subsequent heatingto evolve the water apparently creates very fine pores in the fiber, smaller than if a mineral acid or water alone were used for the treatment. As a theory it appears that each pore created in the fibers picks up both water and some of the metal from the chloride and upon the ultimate evaporation of the water, metal oxide partially fills each pore creating an extremely minute pore condition in the fiber. The solutions, such as chro-mic anhydride (Gro are then highly attracted to the pores and the solute, such as the chromic anhydride, completes the filling of the pore. Upon subsequent drying and heating of the fiber the adsorbed solute is converted to a temperature-resistant oxideCr O in the case of chromic anhydride-and the fiber composed of SiO CaO and Cr- O is both flexible and resistant to temperatures in excess of 2200 F.

The fibers containing the silica and metallic oxide, after expulsion of the water, may be exposed to the chromic anhydride (CrO solution in such manner as to provide on the fibers a complete coverage to the extent that when the material is fired and the insoluble chromic oxide attained, the material will resist, withoutdeformation, temperatures of about 3000" F. Wherethe mass of fibers is compact the temperature-resistant, insoluble oxide penetrates between and is held by the fibers and the product is then resistant to temperatures well in excess of 3000 F.

The fibers which are most useful in the practice of the invention are conveniently termed micro fibers as their the fiber substantially completely, and the alkali constitof reaction with the solutions such as those indicated hereinbet'orc.

Other objects and advantages of the invention will become more apparent during the course of the following description when taken in connection with the accompanying drawings.

in the drawings wherein like numerals are employed to designate like parts throughout the same:

Figure 1 illustrates schematically apparatus useful in producing a mat of fibers;

Figure 2 illustrates schematically apparatus useful in the conversion of fibers of alkali silicate to metallic oxide containing fibers of this invention;

Figure 3 illustrates a loose mass of fibers produced in accordance with the invention; and

Figure 4 illustrates a refractory product in the form of a mass of fibers produced in accordance with this invention.

Referring to the drawings and initially to Figure 1 there is indicated by the numeral 1 a pot retaining a body of molten glass 3, which pot is surrounded by insulating material 5 having induction heating coil 7 therein. The induction heating coil '7 is supplied from a suitable source of energy (not shown) for maintaining the body 3 molten.

The pot P. is provided at 9 with tips through which molten glass exudes to be drawn into filaments ll. Filaments 11 are drawn over guide roll 13 by the action of cooperating drawing rolls i5, 17, and the filaments in parallel arrangement are presented over the lower edge of guide block 19 to the hot gaseous blast 21 emanating from the burner 23. A mixture of air and natural gas, for example, is provided through conduit 24 to the burner 23 and the gases are burned completely within the burner before issuing as the blast 21.

The filaments are softened and attenuated by the heat and force ofthe blast into fine fiber form and are blown through the conduit 25' and received on one leg of screen belt 26, which belt is itself mounted on rollers 27, one of which may be driven in any suitable manner, to effect movement of the belt.

As indicated in the drawing there is provided at 29 a vacuum conduit for attracting the fibers to the belt, and the fibers tend to build up at the lower edge to form a fiuify mass in mat form as indicated at 31.

In the practice of this invention the composition of the molten glass 3 is most suitably an alkali silicate, and preferably sodium silicate. I have found that a composition containing 78.2 silica and 21.8 sodium oxide is highly useful. Thus the flame blown fibers of the mat 31 are constituted essentialy of sodium silicate.

Referring now to Figure 2 there is shown at 33 a container over which there is mounted a motor 34 and from the lower end of the shaft of which there is mounted a stirrer 35. The container 33 retains dispersed fibers of sodium silicate 36 in a solution of calcium chloride 38, and in the practice of this invention the calcium chloride solution may have a concentration of about 5 percent by weight, for example. Preferably a ratio of sodium silicate fibers in the slurry of the container 33 is such that there are about 60 grams of sodium silicate fibers per grams of calcium chloride.

The effect of the calcium chloride solution is to remove the alkali, in this case the sodium constituent, from uent is replaced by a combination of the calcium and water molecules. Thus the slurry 37 after being stirred for approximately 2 hours contains silica, unrcacted calcium chloride, sodium chloride of reaction and water molecules, and the same is run through conduit 39 by simply opening the valve 4-1. Positioned beneath the conduit 39 is a belt 43 mounted on rollers 45 and driven through any suitable source of power (not shown).

A vacuum pan which is positioned beneath the belt is indicated at 4-7 and assists the withdrawal of liquid from the slurry as it passes tothe belt to assume the form of a mat 49. The mat 49 as indicated in Figure 2 is moved rightwardly over the belt 48 into oven 50 operating at a temperature of about 1000 to 1200 degrees Farenheit. The belt 48 is mounted on rollers to and driven by any suitable means (not shown).

The mat is advanced in the process of invention to a. tank 51 containing a solution 53, which in the present instance may suitably be a 0.2 molal solution of chromic anhydride (CrO The mat as it passes through the solution is guided by rollers 55 and supported by rollers 61. As indicated at 57, 59, there may be provided squeeze rolls to prevent an excessive amount of solution from passing out of the tank 51 with the mat. it is to be noted that the fibers of the mat are in close adhering and interlaced relation and the product, while compact, nevertheless is porous and entrains a very considerable amount of air and consequently is of low density.

In the process of the invention the mat is then most suitably conducted to an oven 63 and is supported in its passage to the oven by rollers as at 62. The temperature of 1800-2000 F. of the oven 63 is suificient to convert the chromic anhydride (CrO to a water insoluble condition in which the product is substantially all chromic sesquioxide (Cr O A knife 64 supported abovea table 65 cuts the mass of fibers into a suitable size as the product emerges from the oven. The mat w is drawn through the oven 63 by the cooperating belts 67, 69, which are relatively vertically adjustable as indicated at '70; the drawing is effected at a rate of about 15 feet per minute, sufficient to completely effect a saturation of the mat 49 in the bath 53 and sufiicient also to insure that the mat will be free of any combined water molecules by the action of the oven 50. The chromic anhydride (CrO replaces the water molecules driven out of the pores of the fibers and accordingly the pores of the product are filled with a combination of calcium oxide and water insoluble, temperature-resistant chromic sesquioxide ((3 0 An enlarged view of such a product is indicated in Figure 3.

When the pores of the product indicated at 71 in Figure 3 are similarly filled with the temperature-resistant oxide and when there is no substantial deposition of oxide over the remaining portion of the fibers, the fiber is flexible and the temperature resistance is well above 2200 F., that is, there is no softening at the latter temperature.

If desired a compressed product such as that illustrated in Figure 4 may be attained by running the mat more slowly through the bath 6?) and compressing the product as it passes through the oven. Such a material when baked at a temperature of 3000 Pa, for example, does not soften and the oxide is converted to the water insoluble form. Such a product is useful as a refractory material in the form of the brick indicated at 73 in Figure 4, wherein it may be seen the fibers as are surrounded completely by a temperature-resistant oxide 7d. With the more concentrated solution and longer immersion a greater amount of the solution tends to be physically retained by and-between the fibers.

4. ample of 3-5 feet per minute may be utilized to give time for greater pick-up of the chromic anhydride. The permeation of the mass of fibers is then substantially complete.

While the invention has been specifically described with relation to chromic anhydride (CrO as the material which forms the temperature-resistant oxide, other solutions such as cobalt nitrate (2 molal); zinc chloride (2 molal); aluminum sulfate (0.2 molal); tin chloride (.65 molal); or ferric chloride (1 molal) may be utilized. The data indicates the preferred concentrations of such solutions for the attainment of a block of a refractory as indicated in Figure 4.

it is further to be noted that in a refractory brick structure, such as that shown in Figure 4, the proportion of temperature-resistant oxide is generally between about 6-16 percent by weight of the product; a typical analysis of the fiber of the product indicated at 49 is:

Constituent: Percent by weight If the initial sand from which the sodium silicate is formed contains a slight impurity, sucn as a .25 percent of iron, this may be carried through the procedure and it will appear in the final product, but is not detrimental thereto.

From the foregoing it will be seen that since the water in the flexible fiber is replaced by the temperature-resistant oxide there will be approximately 7 percent of such oxide in the final fiber itself, and since both calcium oxide and the other oxides, such as those of cobalt, chromium, aluminum and zinc, are highly temperatureresistant, the final product is itself resistant to temperature.

A compressed temperature-resistant block which is resistive to temperatures in excess of 3000 F. without fiber fusion, such as that shown in Figure 4, may have a density of 5 to 8 pounds per cubic foot, with a temperature-resistant oxide content of 10 to 12 percent.

With respect to the slurry 37, salts of other metals of the second group of the periodic table, particularly barium chloride and Zinc chloride may be substituted for the calcium if desired.

The thorough removal of the alkali oxide from the alkali silicate and replacement with the oxide of a metal of the second group of the periodic table not only yields a controlled pore size but further provides in the mat 49 (Figure l) a product completely stable at temperatures below 1000 F. and fibers which as to fiber form are stable at temperatures of 2200 F.

The fibers are colored when the temperature-resistant oxide is colored and thus the procedure is adapted for attaining colored products in which the coloring material is intimately bound to and in fact a part of the fiber.

Other alkali silicates particularly potassium silicate may be utilized in the practice of the procedure; lithium silicate has been employed and lower concentrations of silica in sodium silicate such as about percent silica and 30 percent sodium oxide have been found very satisfactory.

It is to be understood that the form of the invention herewith shown and described is to be taken as .a preferred embodiment of the same, but that various changes in the shape. size and arrangement of parts may be resorted to without departing from the spirit of the invention or the scope of the subjoined claims.

I claim:

l. A mass of fibers of micro diameter which fibers are composed of silica, said fibers having a first coating of an oxide of a metal selected from the second group of the periodic table and a second coating of a temper attire-resistant water insoluble oxide of a metal selected from the group consisting of chromium, cobalt, aluminum, tin and iron.

2. A mass of fibers of icro diameter which fibers are composed of silica, said fibers having a first coating of an oxide selected from the group of CaO, BaO and ZnO, and a second coating of a temperatureresistant, water insoluble oxide of chromium.

3. A mass of fibers of micro diameter which fibers are composed of silica, said fibers having a first coating of an oxide selected from the group of CaO, BaO and ZnO, and a second coating of a temperature-resistant oxide of cobalt.

4. A mass of fibers of micro diameter which fibers are composed of silica, said fibers having a first coating of an oxide selected from the group of CaO, Bat) and ZnO, and a second coating of a temperature-resistant oxide of a metal selected from the group consisting of chromium, cobalt, aluminum, tin and iron.

5. A mass of fibers of micro diameter which fibers are composed of SiO said fibers having a first coating of an oxide selected from the group of CaO, BaO and ZnO, and a second coating of a temperature-resistant, water insoluble oxideof a metal selected from the group consisting of chromium, cobalt, aluminum, tin and iron, in which the SiO is present to the extent of at least about 60% by weight, the temperature-resistant oxide is present to the extent of at least about by weight and the balance is essentially an oxide or oxides selected from the group of BaO, CaO, and ZnO.

6. The method which comprises subjecting micro fibers of an alkali silicate to a metallic constituent containing solution to displace the alkali from the fiber and to replace a portion of the alkali with the metallic constituent of the solution, thereafter removing the fiber from the solution and heating the same above about 1000 F. to expel all water therefrom and to provide the fiber with a multiplicity of pores, treating the fiber with a solution containing a metallic constituent which is convertible by heat to a temperature-resistant oxide to cause the adsorption into the pores of the solute of the solution, remov ing the fiber from the solution, and heating the fiber to convert the adsorbed solute to a temperature-resistant oxide.

7. The method which comprises subjecting micro fibers of an alkali silicate to a solution of calcium chloride to eliminate the alkali from the fiber and to replace a portion of the alkali with calcium, thereafter removing the fiber from the solution and heating the same above about 1000 F. to expel all water therefrom and to provide the fiber with a multiplicity of pores, treating the fiber with a solution containing a metallic constituent which is convertible by heat to a temperature-resistant oxide to cause the adsorption into the pores of the solute of the solution, removing the fiber from the solution, and heating the fiber to convert the adsorbed solute to a temperature-resistant oxide.

8. The method which comprises subjecting micro fibers of an alkali silicate to a solution of calcium chloride to eliminate the alkali from the fiber and to replace a portion of the alkali with calcium, thereafter removing the fiber from the solution and heating the same above about 1000 F. to expel all water therefrom and to provide the fiber with a multiplicity of pores, treating the fiber with a solution containing chromic anhydride which is convertible by heat to a water and temperature-resistant oxide to cause the adsorption into the pores of the chromium anhydride of the solution, andheating the fiber to convert the chromic anhydride to a water insoluble temperatureresistant oxide of chromium.

9. As an article of manufacture a refractory product composed of fibers consisting of silica, said fibers having a first coating of an oxide of a metal Selected from the second group of the periodic table, and a second coating of a temperature-resistant oxide of a metal selected from the group consisting of chromitun, cobalt, aluminum, tin and iron, the fibers being covered with the temperature-resistant oxide to an extent sufiicient to inhibit fusion of the fibers at a temperature of 3000 F. v

10. As an article of manufacture, a light weight refractory product composed of a mass of fibers consisting of silica, said fibers having a first coating of calcium oxide and a second coating of chromic oxide, the fibers being surrounded by the chromic oxide to an extent sufficient to inhibit fusion of the fibers at a temperature of about 3000 F.

11. As an article of manufacture, a light Weight refractory product composed of a mass of fibers consisting of silica, said fibers having a first coating of barium oxide and a second coating of chromic oxide, the fibers being surrounded by the chromic oxide to an extent sufficient to inhibit fusion of the fibers at a temperature of about 3000 F.

12. As an article of manufacture, a light weight refractory product composed of a mass of fibers consisting of silica, said fibers having a first coating of zinc oxide and a second coating of chromic oxide, the fibers being surrounded by the chromic oxide to an extent sufiicient to inhibit fusion of the fibers at a temperature of about 3000 F.

13. The method of producing a refractory product containing fibers which method includes extracting with a metallic constituent containing solution the alkali of a mass of alkali silicate fibers to replace a portion of the alkali with the metallic constituent, removing the mass of fibers from the solution and heating above 1000 F. to expel all water from the fibers and to provide fine pores in the fibers, treating the mass of fibers with a solution containing a solute which is convertible by heat to a temperature-resistant oxide to an extent sufiicient to fill the pores and to cover the fibers with the solute, removing the mass of fibers from the solution, and firing the mass to provide a temperature-resistant water insoluble oxide on the fibers.

14. A mass of fibers of micro diameter composed of silica, said fibers having a first coating of an oxide selected from the group consisting of Cat), BaO, ZnO,

and a second coating of a temperature-resistant oxide of a metal selected from the group consisting of chromium, cobalt, aluminum, tin and iron, in which the silica of the fibers is present to the extent of 60-80% by weight, 1

the temperature-resistant oxide is present to the extent of at least about 10% by weight, and the balance is essentially an oxide or oxides from the group of CaO, BaO and ZnO.

15. A mass of fibers of micro diameter composed of silica, said fibers having a first coating of an oxide selected from the group consisting of CaO, BaO and ZnO, and a second coating of a temperature-resistant oxide of a metal selected from a group consisting of chromium, cobalt, aluminum, tin and iron, in which the silica of the fibers is present in about by weight, the temperatureresistant oxide is present in about 14% by weight, and the balance is essentially an oxide or oxides from the group of CaO, BaO and ZnO.

References Cited in the file of this patent UNITED STATES PATENTS 2,303,756 Nordberg et a1. Dec. 1, 1942 2,331,944 VanPazsiczky et a1. Oct. 19, 1943 2,461,841 Nordberg Feb. 15, 1949 2,491,761 Parker et a1. Dec. 20, 1949 2,584,763 Waggoner Feb. 5, 1952 2,593,818 Waggoner Apr. 22, 1952 2,617,742 Olson Nov. 11, 1952 FOREIGN PATENTS 458,115 Great Britain Dec. 14, 1936 

1. A MASS OF FIBERS OF MICRO DIAMETER WHICH FIBERS ARE COMPOSED OF SILICA, SAID FIBERS HAVING A FIRST COATING OF AN OXIDE OF A METAL SELECTED FROM THE SECOND GROUP OF THE PERIODIC TABLE AND SECOND COATING OF A TEMPERATURE-RESISTANT WATER INSOLUBLE OXIDE OF A METAL SELECTED FROM THE GROUP CONSISTING OF CHROMIUM, COBALT, ALUMINUM, TIN AND IRON. 